A device described in Patent Document 1 (hereinafter referred to as the device of Patent Document 1) is an example of a conventional laser welding inspection device. The device of Patent Document 1 is provided with a laser irradiation head that radiates a laser generated by a laser oscillator to a workpiece and welds the workpiece. The laser irradiation head is equipped with a lens (condenser lens) that condenses the laser generated by the laser oscillator and irradiates the laser to the workpiece, and a protective cover that protects the condensing lens from scatterings (evaporated substances contained in the workpiece and the like) generated during the welding. The device of Patent Document 1 is further provided with an optical fiber that is arranged at a position slightly apart from an optical path of the laser irradiated from the laser irradiation head, and a solar battery that is disposed at a position opposite an end of the optical fiber converts light energy into electrical energy (voltage).
According to the device of Patent Document 1, when there are few or no stains or the like on the protective cover, there is little or no scattering of the laser due to stains or the like. As a consequence, a smaller part of the laser irradiates the solar battery and an effective laser is irradiated to the workpiece. However, when there are many stains or the like on the protective cover, more of the laser is scattered by the stains or the like. Thus, much scattered light (laser) is irradiated to the solar battery through the optical fiber and less of the laser is applied to the welding. As a result, an effective laser is not irradiated to the workpiece.
Thus according to the device of Patent Document 1, when there are few or no stains or the like on the protective cover, an effective laser is irradiated to the workpiece and therefore the welding is judged as good. When there are many stains or the like on the protective cover, an effective laser is not irradiated to the workpiece and therefore the welding is judged as poor.
Patent Document 1: Japanese Patent Application Publication No. JP-A-H11-320144